Multi-mode fiber amplifier

Patent metadata

Field	Value
Publication number	US-9570880-B2
Application number	US-201414174269-A
Country	US
Kind code	B2
Filing date	Feb 6, 2014
Priority date	Nov 25, 1998
Publication date	Feb 14, 2017
Grant date	Feb 14, 2017

Abstract

A laser utilizes a cavity design which allows the stable generation of high peak power pulses from mode-locked multi-mode fiber lasers, greatly extending the peak power limits of conventional mode-locked single-mode fiber lasers. Mode-locking may be induced by insertion of a saturable absorber into the cavity and by inserting one or more mode-filters to ensure the oscillation of the fundamental mode in the multi-mode fiber. The probability of damage of the absorber may be minimized by the insertion of an additional semiconductor optical power limiter into the cavity.

First claim

What is claimed is:

1. An optical apparatus comprising:
a length of multi-mode optical fiber comprising a gain medium and configured to propagate a fundamental mode;
a length of single mode optical fiber configured to propagate a single mode; and
a splice between the length of multi-mode optical fiber and the length of single-mode optical fiber,
wherein the single mode of the length of single mode optical fiber is matched to the fundamental mode of the length of multi-mode optical fiber.

2. The optical apparatus of claim 1 , wherein an output end of the length of single mode optical fiber is spliced to an input end of the length of multi-mode optical fiber.

3. The optical apparatus of claim 1 , wherein a tapered portion of the length of single mode optical fiber and the length of multimode optical fiber comprises the splice.

4. The optical apparatus of claim 3 , wherein the tapered portion comprises an adiabatic taper.

5. The optical apparatus of claim 3 , wherein the length of multi-mode optical fiber comprises a core, and a diameter of the core at an input end is sufficiently small to provide single mode operation of the length of multi-mode fiber at the tapered portion.

6. The optical apparatus of claim 1 , wherein the length of multi-mode optical fiber comprises a core having a core diameter, and said gain medium is concentrated centrally within a fraction of the core diameter.

7. The optical apparatus of claim 6 , wherein mode coupling into higher-order modes is reduced by gain guiding and the fundamental mode is preferentially amplified.

8. The optical apparatus of claim 1 , wherein the length of multi-mode optical fiber comprises a fiber core having a total fiber core cross-sectional area, and the gain medium is confined in a cross-sectional area of the fiber core which is substantially smaller than the total fiber core cross-sectional area.

9. The optical apparatus of claim 1 , wherein the optical apparatus is disposed in an optical cavity formed between a first mirror and a second mirror.

10. The optical apparatus of claim 9 , wherein the optical cavity further comprises a pair of Faraday rotators.

11. The optical apparatus of claim 1 , wherein the length of multi-mode optical fiber comprises a core having a diameter that is several tens of microns.

12. The optical apparatus of claim 1 , wherein the optical apparatus is configured as a portion of a multi-mode fiber amplifier.

13. The optical apparatus of claim 1 , wherein the splice is used to match the mode of the length single mode fiber to the fundamental mode of the length of multimode fiber.

14. The optical apparatus of claim 13 , wherein the single mode of the length of single mode fiber is matched to the fundamental mode of the length of multimode fiber with an efficiency of approximately 90% or higher.

15. The optical apparatus of claim 1 , wherein a core of the single mode fiber is thermally tapered to match the single mode of the length of single mode fiber to the fundamental mode of the length of multimode fiber.

16. An optical amplifier comprising the optical apparatus of claim 1 , said optical amplifier configured to provide an amplified output substantially in a fundamental mode.

17. The optical amplifier of claim 16 , wherein the length of multi-mode optical fiber comprises a double clad structure, the gain medium is cladding pumped, and the optical amplifier provides output power greater than 10 kW and a near diffraction limited output beam.

18. The optical amplifier of claim 17 , wherein a core diameter of said length of multimode fiber is several tens of microns.

19. The optical amplifier of claim 17 , wherein a core diameter of said length of multi-mode fiber is larger than a core diameter of said length of single mode fiber.

20. An optical apparatus for amplifying light, the apparatus comprising:
a length of multi-mode optical fiber, said multi-mode optical fiber including a gain medium;
an output for receiving amplified light from said length of multi-mode optical fiber;
an energy source for exciting said gain medium; and
an input for providing a beam of light to be amplified within said length of multi-mode fiber, said input comprising a near-diffraction limited laser source, said input optically coupled to said length of multi-mode fiber, said length of multi-mode fiber providing substantially single mode light at the output of said apparatus.

21. A light amplifier comprising:
a length of multi-mode optical fiber, said multi-mode optical fiber including a gain medium;
an energy source for exciting said gain medium; and
an input for providing a near-diffraction limited beam of light to be amplified within said length of multi-mode fiber, said input optically coupled to said length of multi-mode fiber to provide substantially diffraction limited light at the output of said amplifier, said input comprising a near-diffraction limited laser source.

Assignees

• Imra America Inc

Inventors

• Fermann Martin E
• Harter Donald J

Classifications

• H01S3/08045

  Single-mode emission · CPC title

• H01S3/1608

  erbium · CPC title

• H01S3/06737

  Fibre having multiple non-coaxial cores, e.g. multiple active cores or separate cores for pump and gain · CPC title

• H01S3/1618

  ytterbium · CPC title

• H01S3/06708 Primary

  Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering (optical fibres as passive waveguides G02B6/02) · CPC title